/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.bear.net.httpclient.util.commons.codec.net;

import java.io.UnsupportedEncodingException;

import com.bear.net.httpclient.util.commons.codec.DecoderException;
import com.bear.net.httpclient.util.commons.codec.EncoderException;
import com.bear.net.httpclient.util.commons.codec.binary.StringUtils;


/**
 * <p>
 * Implements methods common to all codecs defined in RFC 1522.
 * </p>
 * <p>
 * <a href="http://www.ietf.org/rfc/rfc1522.txt">RFC 1522</a> describes
 * techniques to allow the encoding of non-ASCII text in various portions of a
 * RFC 822 [2] message header, in a manner which is unlikely to confuse existing
 * message handling software.
 * </p>
 * 
 * @see <a href="http://www.ietf.org/rfc/rfc1522.txt"> MIME (Multipurpose
 *      Internet Mail Extensions) Part Two: Message Header Extensions for
 *      Non-ASCII Text</a> </p>
 * @author Apache Software Foundation
 * @since 1.3
 * @version $Id: RFC1522Codec.java 798428 2009-07-28 07:32:49Z ggregory $
 */
abstract class RFC1522Codec {

    /**
     * Separator.
     */
    protected static final char SEP = '?';

    /**
     * Prefix
     */
    protected static final String POSTFIX = "?=";

    /**
     * Postfix
     */
    protected static final String PREFIX = "=?";

    /**
     * Applies an RFC 1522 compliant encoding scheme to the given string of text
     * with the given charset. This method constructs the "encoded-word" header
     * common to all the RFC 1522 codecs and then invokes
     * {@link #doEncoding(byte [])} method of a concrete class to perform the
     * specific enconding.
     * 
     * @param text a string to encode
     * @param charset a charset to be used
     * @return RFC 1522 compliant "encoded-word"
     * @throws EncoderException thrown if there is an error conidition during
     *             the Encoding process.
     * @throws UnsupportedEncodingException thrown if charset is not supported
     * @see <a
     *      href="http://java.sun.com/j2se/1.4.2/docs/api/java/nio/charset/Charset.html">Standard
     *      charsets</a>
     */
    protected String encodeText(final String text, final String charset) throws EncoderException,
            UnsupportedEncodingException {
        if (text == null) {
            return null;
        }
        StringBuffer buffer = new StringBuffer();
        buffer.append(PREFIX);
        buffer.append(charset);
        buffer.append(SEP);
        buffer.append(getEncoding());
        buffer.append(SEP);
        byte[] rawdata = doEncoding(text.getBytes(charset));
        buffer.append(StringUtils.newStringUsAscii(rawdata));
        buffer.append(POSTFIX);
        return buffer.toString();
    }

    /**
     * Applies an RFC 1522 compliant decoding scheme to the given string of
     * text. This method processes the "encoded-word" header common to all the
     * RFC 1522 codecs and then invokes {@link #doEncoding(byte [])} method of a
     * concrete class to perform the specific deconding.
     * 
     * @param text a string to decode
     * @return A new decoded String or <code>null</code> if the input is
     *         <code>null</code>.
     * @throws DecoderException thrown if there is an error conidition during
     *             the Decoding process.
     * @throws UnsupportedEncodingException thrown if charset specified in the
     *             "encoded-word" header is not supported
     */
    protected String decodeText(final String text) throws DecoderException,
            UnsupportedEncodingException {
        if (text == null) {
            return null;
        }
        if ((!text.startsWith(PREFIX)) || (!text.endsWith(POSTFIX))) {
            throw new DecoderException("RFC 1522 violation: malformed encoded content");
        }
        int terminator = text.length() - 2;
        int from = 2;
        int to = text.indexOf(SEP, from);
        if (to == terminator) {
            throw new DecoderException("RFC 1522 violation: charset token not found");
        }
        String charset = text.substring(from, to);
        if (charset.equals("")) {
            throw new DecoderException("RFC 1522 violation: charset not specified");
        }
        from = to + 1;
        to = text.indexOf(SEP, from);
        if (to == terminator) {
            throw new DecoderException("RFC 1522 violation: encoding token not found");
        }
        String encoding = text.substring(from, to);
        if (!getEncoding().equalsIgnoreCase(encoding)) {
            throw new DecoderException("This codec cannot decode " + encoding + " encoded content");
        }
        from = to + 1;
        to = text.indexOf(SEP, from);
        byte[] data = StringUtils.getBytesUsAscii(text.substring(from, to));
        data = doDecoding(data);
        return new String(data, charset);
    }

    /**
     * Returns the codec name (referred to as encoding in the RFC 1522)
     * 
     * @return name of the codec
     */
    protected abstract String getEncoding();

    /**
     * Encodes an array of bytes using the defined encoding scheme
     * 
     * @param bytes Data to be encoded
     * @return A byte array containing the encoded data
     * @throws EncoderException thrown if the Encoder encounters a failure
     *             condition during the encoding process.
     */
    protected abstract byte[] doEncoding(byte[] bytes) throws EncoderException;

    /**
     * Decodes an array of bytes using the defined encoding scheme
     * 
     * @param bytes Data to be decoded
     * @return a byte array that contains decoded data
     * @throws DecoderException A decoder exception is thrown if a Decoder
     *             encounters a failure condition during the decode process.
     */
    protected abstract byte[] doDecoding(byte[] bytes) throws DecoderException;
}
